The problem is the same in many sports, industries or businesses, not just in football. You can have a great car, but if you don't have a great driver, you won't win prestigious races. You can have a big company, but if your CEO makes the wrong calls or implements the wrong strategy, your company won't be as successful as it could be.
It's the same for PSG. It's one of the main reasons (if not the main one) why, despite the heavy investment, the team has failed to do better than the quarterfinals in the Champions League. It's because they never had the right man at the helm.
Unless you are Roberto Di Matteo and have an incredible group of players who are pretty much in charge of everything (Chelsea 2012), you won't win the Champions League without a top manager. Two-time winner Zinedine Zidane has done enough to be included in this category while Luis Enrique (Barcelona 2015) was able to revitalise a struggling Barca team.
Carlo Ancelotti (Real Madrid 2014, Milan 2007), Jupp Heynckes (Bayern 2013), Pep Guardiola (Barcelona 20011, 2009), Jose Mourinho (Inter 2010, Porto 2004), Sir Alex Ferguson (Manchester United 2008) and Rafael Benitez (Liverpool 2005) are all part of the elite.
In the last four-and-a-half years, Laurent Blanc and Unai Emery have not been good enough. They were never going to be good enough to compete with top managers, simply because they are not top managers. PSG were hoping that they would reach that point, but instead they kept making mistakes.
The Qatari owners of PSG have spent a lot of time and even more money to build teams that could compete to win the Champions League. When they took over the club in the summer of 2011, their plan was to reach the Graal (Grail) within five years. They are already two years late.
They were too ambitious, but there is nothing wrong with that. However, you need a plan to back it up. In this case, it seems to have been more about the players than the managers. Buying top players is not easy, but it is way harder to convince a top manager that your project, the environment around your club and your strategy are good enough to make you win trophies quickly. Especially when you don't have a tradition of success at the highest level.
PSG did try, though. After Ancelotti left for Real Madrid in the summer of 2013 after just 18 months in charge (and a narrow defeat on away goals to a much more experienced Barcelona team in the quarterfinals), they could not get any of their main targets. They tried to get Mourinho, Arsene Wenger, Benitez, Manuel Pellegrini and Fabio Capello. Blanc was a choice by default, and it showed.
Despite some good performances in Europe, Blanc messed everything up against Chelsea in 2014 and, more importantly, vs. Manchester City a year later, notably by playing a back three for the first time all season. That City game was a disaster and showed that Blanc was out of his depth. So you thought that once they got rid of him, they would make sure that their next manager was a better fit.
Well, they failed again.
Emery did some great things at Sevilla but doesn't have the man-management skills, the name or the pedigree to get the full respect of a tough dressing room. A disastrous 6-1 defeat away at Barcelona in the second leg of last season's Round of 16 last season showed his limits and the first leg in Madrid this campaign -- a 3-1 defeat -- exposed his flaws again.
Ultimately, the players are the ones on the pitch, and they weren't good enough against Real Madrid. They made stupid mistakes in both games, which are not the manager's fault, but he didn't help by losing his tactical battle with Zidane.
So, what's next? Emery will not get a third season in Paris. He will be gone in the summer, and replacing him with the right manager is probably the biggest decision Nasser al Khelaifi, the PSG chairman, will have to make since arriving at the club.
In terms of players, PSG have gone forward since 2011. Of course, there are still some issues and weaknesses in terms of characters and personnel, but the current squad is better than the 2012 or the 2016 ones. In terms of managers, however, they have gone backwards.
There will be a lot of candidates to take charge in the summer, some good and some not so good. This time, they have to get it right.